A method (1) creates charge carriers in a concentration that changes in a periodic
manner (also called "modulation") only with respect to time, and (2) determines
the number of charge carriers created in the carrier creation region by measuring
an interference signal obtained by interference between a reference beam and a
portion of a probe beam that is reflected by charge carriers at various depths
of the semiconductor material, and comparing the measurement with corresponding
values obtained by simulation (e.g. in graphs of such measurements for different
junction depths). Various properties of the reflected portion of the probe beam
(such as power and phase) are functions of the depth at which the reflection occurs,
and can be measured to determine the depth of the junction, and the profile of
active dopants. Therefore, the just-described reflected portion of the probe beam
is interfered with a reference beam formed by a portion of probe beam reflected
by the front surface of the semiconductor material, and phase and amplitude of
the interference signal resulting therefrom are both measured. Alternatively, a
phase difference between a first interference signal (obtained by interference
of (1) a variable phase beam and (2) the portion of probe beam reflected by the
front surface) and a second interference signal (obtained by interference of (1)
the variable phase beam and (2) a portion of the probe beam reflected by charge
carriers at various depths) indicates the junction depth.
